Customers or users of large amounts of electric power typically consume such power at uneven or sporadic rates. This is especially true for customers with highly punctuated loads, that is, having many pieces of equipment with frequent stops and starts. Such customers can be expected to build random and cumulative peaks in their power demands.
A typical daily load profile for many industrial manufacturing facilities, retail establishments, and the like, is made up of several randomly acting loads, such as shown in prior art FIGS. 1A-1D. FIG. 1A illustrates a constant twenty-four hour lighting load. FIG. 1B illustrates semi-random punctuated load. FIG. 1C illustrates semi-random longer cycle loads. FIG. 1D illustrates a composite idealized daily load profile, showing high stochastic peaks arising randomly throughout the day.
Despite these fluctuating demands for electric power, electric utilities (e.g. PEPCO) are required to maintain a generating capacity that exceeds the maximum demand for electricity anticipated during any given period of time. Therefore, electric utilities must maintain generating capacities far in excess of average electric power requirements in order to meet such occasional and relatively short term demands. The formation and maintenance of such excess capacities is quite expensive, dramatically increases the average cost of providing electric power to customers, and create excessive pollution in the environment.
In order to better allocate the cost of providing excess power generation capacity to those customers most requiring such capacity, and in order to encourage such customers to distribute their demand for electric power, the utility rates schedule to such customers is typically divided into at least two components. The first component is an energy usage charge which reflects the utility's own energy generation and transmission costs. This charge is typically calculated in cents per kilowatt (KW) hour of energy consumed during a particular billing period. The second component of the bill is a peak demand charge which reflects the utility's capital costs, and is based on the deviation from average energy consumed by the customer during a predetermined demand interval period of time. The peak demand charge is calculated as cents, or dollars, per kilowatt of actual peak demand. Such peak demand charges can be quite high as a percentage of the total utility charge over a predetermined billing period.
Owing to the increased use of greater peak demand charges by electric utilities, large consumers of electricity have begun investigating methods for reducing peak power demands from the utility. One approach is sequencing equipment use so that only an acceptable predetermined number of load contributors are allowed to operate simultaneously. Unfortunately, this method is expensive to control and restrictive to customers.
U.S. Pat. No. 5,369,353 discloses an apparatus that stores energy during periods when excess supply is available, and then releases that energy during times of higher demand. Unfortunately, the apparatus of the '353 patent utilizes a battery, for example, for the energy storage device. The use of a battery for this application is expensive and burdensome, and requires the addressing of recharging issues, replacing such batteries, the expensive nature of the batteries themselves, etc.
U.S. Pat. No. 5,500,561 discloses a power management system including primary and secondary sources of electricity. The system senses peak power demands for electricity and switches a particular load of the customer to a secondary source (e.g. storage battery) so as to reduce peak power demands. Unfortunately, a secondary source disclosed in the '561 patent is also a battery. Thus, the system of the '561 patent suffers from problems similar to those discussed above relating to the '353 patent. Batteries as providers of secondary electricity are undesirable.
It is apparent from the above that there exists a need in the art for a power management system, including a secondary or auxiliary source, that is more cost effective and simpler to utilize than those discussed above.
This invention will now be described with respect to certain embodiments thereof, accompanied by certain illustrations, wherein: